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Davis Vantage
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FIRE DANGER RATING

A fire danger rating system should supply an objective answer to
the question: 'What is the probability of a fire starting, spreading and
doing damage today?' It enables fire managers to properly assess the
levels of preparedness and the suppression resources needed to keep fire
losses to a minimum. A fire danger rating system measures the variable
elements which cause day to day changes in fire risk, and interprets the
information gained. The information is used to:

To interpret the system the three fuel moisture codes and the three
behaviour indices need to be understood. Each code and index is a
numerical rating related to likely fire behavior. The scales start at
zero, and except for the Fine Fuel Moisture Code which has a maximum of
99, all are open-ended. Low ratings indicate high moisture content, and
ratings rise as moisture content decreases. Ratings rise as fire weather
becomes more severe.

This is a numerical rating of the moisture content of surface
litter and other cured fine fuels. It shows the relative ease of
ignition and flammability of fine fuels. The moisture content of fine
fuels is very sensitive to the weather. Even a day of rain, or of fine
and windy weather, will significantly affect the FFMC rating. The system
uses a time lag of two-thirds of a day to accurately measure the
moisture content in fine fuels. The FFMC rating is on a scale of 0 to
99. Any figure above 70 is high, and above 90 is extreme.

Duff Moisture Code – DMC

DMC is a numerical rating of the average moisture content of
loosely compacted organic layers of moderate depth. The code indicates
the depth that fire will burn in moderate duff layers and medium size
woody material. Duff layers take longer than surface fuels to dry out
but weather conditions over the past couple of weeks will significantly
affect the DMC. The system applies a time lag of 12 days to calculate
the DMC. A DMC rating of more than 30 is dry, and above 40 indicates
that intensive burning will occur in the duff and medium fuels. Burning
off operations should not be carried out when the DMC rating is above
40.

Drought Code – DC

The DC is a numerical rating of the moisture content of deep,
compact, organic layers. It is a useful indicator of seasonal drought
and shows the likelihood of fire involving the deep duff layers and
large logs. A long period of dry weather (the system uses 52 days) is
needed to dry out these fuels and affect the Drought Code. A DC rating
of 200 is high, and 300 or more is extreme indicating that fire will
involve deep sub-surface and heavy fuels. Burning off should not be
permitted when the DC rating is above 300.

Fire Behaviour Indices

The three behaviour indices are relative to the fuel moisture
content. They indicate what a fire is likely to do. The lower the
moisture content, the higher the Fuel Moisture Codes, and the higher the
Fire Behaviour Indices – and the more active the fire will be.

Initial Spread Index – ISI

This indicates the rate fire will spread in its early stages. It is calculated from the FFMC rating and the wind factor.
The open-ended ISI scale starts at zero and a rating of 10
indicates high rate of spread shortly after ignition. A rating of 16 or
more indicates extremely rapid rate of spread.

Build -Up Index – BUI

This index shows the amount of fuel available for combustion,
indicating how the fire will develop after initial spread. It is
calculated from the Duff Moisture Code and the Drought Code.
The BUI scale starts at zero and is open-ended. A rating above 40 is high, above 60 is extreme.

Fire Weather index - FWI

Information from the ISI and BUI is combined to provide a numerical
rating of fire intensity – the Fire Weather Index. The FWI indicates
the likely intensity of a fire.

The FWI is divided into five fire danger classes:

Index

Low

Moderate

High

Very High

Extreme

FFMC

0-81

81-88

88-90.5

90.5-92.5

92.5+

DMC

0-13

13-28

28-42

42-63

63+

DC

0-80

80-210

210-274

274-360

360+

ISI

0-4

4-8

8-11

11-19

19+

BUI

0-19

19-34

34-54

54-77

77+

FWI

0-5

5-14

14-21

21-33

33+

Interpreting The Information

1. The moisture codes (FFMC, DMC and DC) indicate what fuels will
be involved and their ease of ignition. This will vary during the
season. Each code must be considered to assess potential burning
characteristics.

Example: 1

FFMC = 86 DMC = 25 DC = 120

These ratings indicate:

* fine fuels will ignite easily
* fire will involve the light fuels and to a limited extent the medium and duff layer fuels
* fire will not become deep seated

NexradItâ€™s the "NEXt generation weather RADar", a nationwide network of 120 Doppler radars being used by National Weather Service meteorologists to detect precipitation, to measure atmospheric motions and to issue warnings of severe weather.

Some information is provided by a private weather station and is not an officially recognized station for weather reporting. Though we strive to achieve accurate reporting for our own use it is important that you doNOTdepend on the data provided here for any purpose.